In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles, particularly the development of electric and hybrid drive systems for improved fuel efficiency. In most hybrid or electric vehicles, high-voltage energy storage systems are utilized to improve efficiency. These high-voltage energy storage systems may capture energy within the powertrain system, for example, by using regenerative braking to convert kinetic energy to electrical energy and storing the electrical energy. Additionally, the high-voltage energy storage systems may store electrical energy supplied from a power supply or charger.
Because of the power capacity of the high-voltage energy storage systems and the desire to retain energy for long periods of time, it is therefore desirable that these high-voltage energy storage systems remain primarily disconnected from other devices and connected as needed. Often, contactors or similar connection mechanisms are used to connect vehicle devices to the high-voltage energy storage systems. However, if the high-voltage energy storage system is connected directly to a device which has an electrical potential that differs from the electrical potential of the energy storage system, a large inrush current will occur. This inrush current may potentially damage electrical components or weld the contactors shut, such that the contactors remain in a permanently closed state.
Accordingly, systems have developed that utilize inrush current limiting to connect the high-voltage energy storage systems with vehicle devices. Most of these systems utilize a precharge resistor connected in series with an additional precharge contactor that is connected to the device. The precharge contactor is closed, allowing a limited current to flow to the device based on the precharge resistor and the RC characteristics of the combined system. Once the voltage supplied to the device reaches a stable level, another contactor is closed and the precharge contactor is opened, thereby removing the precharge resistor from the circuit. These systems often incorporate additional hardware or software to monitor the voltage supplied to the device. Furthermore, there is a delay inherent to these precharge systems, because the RC time constant of these precharge systems governs the time required before connecting the device and transferring high-voltage energy to/from the energy storage system.